How small cosmic seeds grow into big stars

New images from the Smithsonian’s Submillimeter Array (SMA) telescope provide the most detailed view yet of stellar nurseries within the Snake nebula. These images offer new insights into how cosmic seeds can grow into massive stars.

These two panels show the Snake nebula as photographed by the Spitzer and Herschel space telescopes. At mid-infrared wavelengths (the upper panel taken by Spitzer), the thick nebular material blocks light from more distant stars. At far-infrared wavelengths, however (the lower panel taken by Herschel), the nebula glows due to emission from cold dust. The two boxed regions, P1 and P6, were examined in more detail by the Submillimeter Array (SMA).Credit: Spitzer/GLIMPSE/MIPS, Herschel/HiGal, Ke Wang (ESO)

Stretching across almost 100 light-years of space, the Snake nebula is located about 11,700 light-years from Earth in the direction of the constellation Ophiuchus. In images from NASA’s Spitzer Space Telescope, which observes infrared light, it appears as a sinuous, dark tendril against the starry background. It was targeted because it shows the potential to form many massive stars (stars with more than 8 times the mass of our Sun). SMA was used to observe sub-millimetre radiation from the nebula, radiation emitted between the infrared and radio parts of the electromagnetic spectrum.

“To learn how stars form, we have to catch them in their earliest phases, while they’re still deeply embedded in clouds of gas and dust, and the SMA is an excellent telescope to do so,” explained lead author Ke Wang of the European Southern Observatory (ESO), who started the research as a predoctoral fellow at the Harvard-Smithsonian Center for Astrophysics (CfA).

The team studied two specific spots within the Snake nebula, designated P1 and P6. Within those two regions they detected a total of 23 cosmic “seeds” — faintly glowing spots that will eventually give birth to between one and a few stars. The seeds generally weigh between 5 and 25 times the mass of the Sun, and each spans a few hundred billion kilometres (for comparison the average Earth-Sun distance is 150 million km). The sensitive, high-resolution SMA images not only unveil the small seeds, but also differentiate them in age.

Previous theories proposed that high-mass stars form within very massive, isolated “cores” weighing at least 100 times the mass of the Sun. These new results show that that is not the case. The data also demonstrate that massive stars aren’t born alone but in groups.

“High-mass stars form in villages,” said co-author Qizhou Zhang of the CfA. “It’s a family affair.”

The team was surprised to find that these two nebular patches had fragmented into individual star seeds so early in the star formation process. They also detected bipolar outflows and other signs of active, ongoing star formation. Eventually, the Snake nebula will dissolve and shine as a chain of several star clusters.